Magnetic medical devices with changeable magnetic moments and method of navigating magnetic medical devices with changeable magnetic moments

ABSTRACT

A method of navigating a medical device having a changeable magnetic moment within an operating region within a patient, the method includes applying a navigating magnetic field to the operating region with an external source magnet, and changing the direction of the magnetic moment in the medical device to change the orientation of the medical device in a selected direction within the operating region. The magnet moment of the medical device can be created by one or more electromagnet coils, in which case the magnetic moment can be changed by changing the current to the coil. Alternatively, the magnetic moment of the medical device can be created by one or more permanent magnets, in which case the magnetic moment can be changed by mechanically or magnetically manipulating the permanent magnet.

This is a continuation of U.S. patent application Ser. No. 09/504,835,filed Feb. 16, 2000, now issued U.S. Pat. No. 6,401,723, issued Jun. 11,2002, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates to the magnetic navigation of medical devices,and in particular to magnetic medical devices with changeable magneticmoments, and to methods of navigating magnetic medical devices withchangeable magnetic moments.

It has long been proposed to magnetically navigate catheters through thebody with an externally applied magnetic field. Recent advances havemade the magnetic navigation of catheters and other medical devicespractical. Typically, the medical device is provided with a permanent ora permeable magnetic element. An external source magnet, which may be apermanent magnet, an electromagnet, or a superconducting electromagnet,is used to apply a magnetic field and/or gradient to an operating regioninside a patient to act on the magnetic element in the medical device toorient and/or move the medical device in the operating region. Themedical device is oriented and/or moved by changing the magnetic fieldand/or gradient applied by the external source magnet.

In the case of stationary electromagnetic and superconductingelectromagnetic source magnets, changing the magnetic field and/orgradient is accomplished by changing the currents supplied to the sourcemagnet. In the case of moveable source magnets, changing the magneticfield and/or gradient is accomplished by changing the position and/ororientation of the source magnet. If the moveable source magnet is anelectromagnet or a superconducting electromagnet, the magnetic fieldand/or gradient can also be changed by changing the current supplied tothe magnet.

While systems with stationary electromagnets and superconductingelectromagnets provide fast, safe, and effective navigation of medicaldevices, it can be expensive to construct and maintain a system thatoperates in real time to provide unrestricted navigation in the body.Similarly while systems with moving source magnets provide fast, safe,and effective navigation of medical devices, it can be expensive toconstruct and maintain a system that can accurately move the sourcemagnets to make a selected change in the magnet field and/or gradient.

The changing fields and gradients created by the source magnets arestrong and will usually require shielding at many health carefacilities. This shielding is another difficulty and expense of magneticnavigation systems that employ changing source magnetic fields andgradients to navigate magnetic medical devices in the body.

While systems using changing source magnet magnetic fields and gradientsprovide precise control and a high degree of navigational flexibility,for some types of medical procedures a less complicated, less expensive,and preferably more compact navigation system would be desirable.

SUMMARY OF THE INVENTION

Generally according to the principles of the present invention amagnetic medical device having a changeable magnetic moment isintroduced into an operating region in the body, a navigating magneticfield is applied to the operating region, and the magnetic moment of themagnetic medical device is changed to orient the magnetic medical devicerelative to the externally applied navigating magnetic field.

As used herein a magnetic medical device having a changeable magneticmoment does not include magnetic medical devices that have a permeablemagnetic material in which a magnetic moment is induced in the permeablemagnetic material by the application of the navigating magnetic field,but only to magnetic medical devices in which the change in the magneticmoment direction is independent from the navigating magnetic field, andthe magnetic moment is acted upon by the navigating magnetic field.

According to the first embodiment of the invention, the magnetic medicaldevice includes at least one electromagnetic coil, and preferable morethan one coil, so that the magnetic moment of the medical device can bechanged by changing the current in the at least one electromagneticcoil. This causes the magnetic medical device to move with respect tothe externally applied navigating magnetic field.

According to a second embodiment, the magnetic medical device includes amoveable permanent magnet, movement of which causes the magnetic momentof the medical device to change. In a first construction or this secondembodiment, the permanent magnet is moved with a mechanism. In a secondconstruction of this second embodiment, the permanent magnet is movedwith one or more electromagnetic coils that selectively create a localmagnetic field to orient the permanent magnet to change the magneticmoment of the magnetic medical device. A lock can be provided toselectively lock the permanent magnet in its selected position.

According to a third embodiment, the magnetic medical device includes amoveable permanent magnet, movement of which causes the magnetic momentof the medical device to change. The permanent magnet is lockable in themagnetic medical device, so that its orientation remains fixed relativeto the magnetic medical device. The orientation of the permanent magnetrelative to the magnetic medical device can be changed by unlocking thepermanent magnet, applying an external configuring magnetic field tochange the orientation of the permanent magnet, and locking thepermanent magnet. The external configuring magnetic field can then beremoved, and an external navigating magnet field applied to orient themagnetic medical device with its new magnetic moment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the distal end of a magnetic medical deviceconstructed according to a first embodiment of this invention;

FIG. 2 is a side elevation view of the distal end of the magneticmedical device of the first embodiment;

FIG. 3 is a transverse cross-sectional view of the magnetic medicaldevice taken along the plane of line 3—3 in FIG. 2;

FIG. 4 is a top plan view of the distal end of a first alternateconstruction of the magnetic medical device of the first embodiment, inwhich the coils comprise multiple coil sections arranged in series;

FIG. 5 is a side elevation view of the distal end of the magneticmedical device of the first alternate construction of the firstembodiment;

FIG. 6 is a transverse cross-sectional view of the magnetic medicaldevice taken along the plane of line 6—6 in FIG. 5;

FIG. 7 is schematic diagram of a second alternate construction of themagnetic medical device of the first embodiment, configured forcirculation of cooling fluid to prevent the coils from overheating;

FIG. 8 is a schematic diagram of third alternate construction of themagnetic medical device of the first embodiment, with flexiblemultistranded leads for conducting heat from the coils to prevent thecoils from overheating;

FIG. 9 is a perspective view of the distal end of a magnetic medicaldevice constructed according to a second embodiment of this invention;

FIG. 10A is a longitudinal cross-sectional view of the distal end of amagnetic medical device of the second embodiment of this invention,showing the permanent magnet in a first orientation;

FIG. 10B is a longitudinal cross-sectional view of the distal end of themagnetic medical device of the second embodiment showing the permanentmagnet in a second position;

FIG. 11 is a transverse cross-sectional view taken along the plane ofline 11—11 in FIG. 10A;

FIG. 12 is a top plan view of the distal end of a magnetic medicaldevice constructed according to a second construction of the secondembodiment of this invention;

FIG. 13 is a side elevation view of the distal end of the magneticmedical device of the second construction of the second embodiment;

FIG. 14 is a transverse cross-sectional view of the magnetic medicaldevice of the second construction of the second embodiment, taken alongthe plane of line 9—9 in FIG. 8;

FIG. 15A is a longitudinal cross-sectional view of the distal end of amagnetic medical device according to a third embodiment of thisinvention, showing the permanent magnet locked in a first position;

FIG. 15B is a longitudinal cross-sectional view of the distal end of themagnetic medical device of the third embodiment, showing the permanentmagnet unlocked in the first position;

FIG. 15C is a longitudinal cross-sectional view of the distal end of themagnetic medical device of the third embodiment, showing the permanentmagnet unlocked in a second position; and

FIG. 15D is a longitudinal cross-sectional view of the distal end of themagnetic medical device of the embodiment, showing the permanent magnetlocked in the second position;

Corresponding reference numbers indicate corresponding parts throughoutthe drawings.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of a magnetic medical device constructed according tothe principles of this invention is indicated generally as 20 in FIGS.1-7. While as shown in FIGS. 1-3 the magnetic medical device 20 is acatheter having a sidewall defining a lumen therein, this invention isnot so limited and the magnetic medical device 20 could be any othermedical device that a physician might want to navigate in the body, suchas an electrode, a biopsy tool, or an endoscope.

The magnetic medical device 20 is preferably an elongate medical devicehaving a proximal end (not shown) and a distal end 24 that is insertedinto and navigated inside the patient's body. The magnetic medicaldevice 20 is preferably sufficiently flexible to allow the distal endportion to flex under the forces generated by external magnetic fieldacting on the magnetic moment of the magnetic medical device to permitnavigation of the device through the body. According to the principlesof this invention, there is at least one coil adjacent the distal end 24of the magnetic medical device 20 which can be selectively energized tochange the magnetic moment near the distal end 24 of the magneticmedical device 20. In the preferred embodiment there are three coils 26,28, and 30, which are preferably arranged in three mutuallyperpendicular planes. The coil 26 is preferably embedded in the wall ofthe magnetic medical device 20 adjacent the distal end 24 and extendscircumferentially around the distal end portion of the magnetic medicaldevice 20. The coil 26 is generally oriented in a plane 30 transverse tothe axis of the magnetic medical device 20. The coil 28 is alsopreferably embedded in the wall of the magnetic medical device 20 nearthe distal end 24. The coil 28 is generally in a plane 32 parallel tothe longitudinal axis of the magnetic medical device 20. The coil 30 islikewise preferably embedded in the wall of the device. The coil 30 isgenerally in a plane 34 parallel to the longitudinal axis of the deviceand perpendicular to the plane 32 in which coil 28 lies.

Leads 36 and 38 extend to coil 26, leads 40 and 42 extend to coil 28,and lead longitudinal 44 and 46 extend to coil 30. The leads 36, 38, 40,42, 44 and 46 allow current to be supplied to coils 26, 28 and 30 tocreate a magnetic moment of a selected direction and intensity. Whilethe coils 26, 28, and 30 are shown arranged in mutually perpendicularplanes, they could be arranged in some other configuration provided thatthe coils provide sufficiently broad selection of magnetic momentdirections for reasonable navigation. Of course, the coils 26, 28, and30 could be provided with either or both a common power supply lead anda common ground lead, to reduce the number of lead extending from thedistal end of the magnetic medical device to the proximal end of thedevice, and to simplify construction.

The magnetic torque on the distal end of the catheter is directlyproportional to the magnetic moment of the magnetic medical device andto the applied navigating magnetic field. For a coil, the magneticmoment is directly proportional to the product of the number of turns inthe coil, the current through the coil, and the cross-sectional area ofthe coil wire. For example, for a typical catheter with diameter of 2mm, the coil 26 may be wound with 1,000 turns of AWG #50 magnet wirehaving a diameter of 0.025 mm. This corresponds to a 5 mm long coil with5 layers having total thickness of 0.125 mm imbedded into the catheterwall. When 0.1 amps of current are applied through this coil, the coilcreates a magnetic moment of 0.4 nano-Tesla-cubic meter. For comparison,a neodymium-boron-iron magnet of a comparable size (5 mm long, 2 mmdiameter, and 0.125 mm thick) has a magnetic moment of about 4nano-Tesla-cubic meter. Thus a coil for creating a variable magneticmoment should be operated in an externally applied navigating magneticfield about ten times that required for a similar sized permanent magnetto achieve the same magnetic torque at the catheter tip.

Currents of 0.1 amps and larger applied continuously through the coilswill typically cause the coil temperature to rise. In many applicationsthe coil is naturally cooled, such as by convention to flowing blood invascular navigation, or by conduction to a static liquid pool of bodyfluid. However, as discussed below, in some applications it may bedesirable to cool the coils by supplying a continuous flow of a coolantwithin the catheter. It may be desirable to provide thermally insulatingmaterial between the coil and the outside surface of the catheter whichcontacts body tissues. Alternatively, or additionally, heat can beconducted away from the distal end 24 of the catheter 20 and distributedthroughout a larger volume of the catheter by providing electrical leadwires that are build up of multiple strands to create a flexible yetmassive thermally conducting conduit, as discussed in more detail below.

Each of the coils 28 and 32 are constructed from 150 turns of AWG #50magnet wire. The coils are 10 mm long with 5 layers imbedded in the wallof the magnetic medical device 20. The total magnetic moment of the twocoils is 0.4 nano-Tesla-cubic meter, the same as the longitudinal coil26.

As shown in FIGS. 4-6, in a first alternate construction of the magneticmedical device of the first embodiment, indicated generally as 20′. Themagnetic medical device 20′ is similar in construction to magneticmedical device 20, except that instead of coil 28, device 20′ has twosub-coils 28 a and 28 b, connected in series and arranged on oppositesides of the magnetic medical device, and that instead of coil 30,device 20′ has two sub-coils 30 a and 30 b, connected in series andarranged on opposite sides of the magnetic medical device. As shown inFIG. 6, the sub-coils 28 a and 28 b are arranged in two generallyparallel planes 32 a and 32 b, and the sub-coils 30 a and 30 b arearranged in two generally parallel planes 34 a and 34 b. The planes 32 aand 32 b are generally perpendicular to the planes 34 a and 34 b.

As noted above, the coils 26, 28, and 30 tend to heat up in use. Attemperatures above about 45°, the coils can be harmful to thesurrounding tissue, and at temperatures above about 50°, the coils cankill surrounding tissue. In some applications, for example navigationthrough the vasculature, the flow of body fluids will sufficiently coolthe coils. In other applications, the coils may need to be activelycooled to prevent harmful heating. A second alternate construction of amagnetic medical of the first embodiment is indicated generally as 20″in FIG. 7. The magnetic medical device 20″ is similar in construction tomagnetic medical device 20, except as shown in FIG. 7 the magneticmedical device 20″ includes a reservoir 50 for storing cooling fluid, apump 52 for circulating cooling fluid, and a tube 54 for deliveringcooling fluid to the distal end of the magnetic medical device to coolthe coils.

Cooling fluid is pumped by pump 52 from reservoir 50 through tube 54 tothe distal end of the magnetic medical device 20″. The cooling fluidreturns to the reservoir 50 in the annulus between the tube 54 and theinternal walls of the magnetic medical device 20″. If necessary, thereservoir can be cooled to cool the cooling fluid.

A third alternate construction of a magnetic medical device of the firstembodiment is indicated generally as 20′″ in FIG. 8. The magneticmedical device 20″ is similar in construction to magnetic medical device20, except as shown in FIG. 8 the magnetic medical device 20′″ hasflexible multistranded leads for the coils to conduct heat proximallyaway from the coils. (Only coil 26 is shown in the schematic view ofFIG. 5, with leads 36′″ and 38′″).

Particularly where the coils are not embedded in the walls of themagnetic medical device, they may be covered with a thermally insulatingpolymer coating to protect tissue that might come into contact with thedistal end of the magnetic medical device.

A second embodiment of a magnetic medical device constructed accordingto the principles of this invention is indicated generally as 100 inFIGS. 9, 10, and 11. As indicated above, the magnetic medical device 100may be any device that a physician might want to navigate through thebody, such as a catheter, an electrode, a biopsy tool, or an endoscope.The magnetic medical device 100 typically has a proximal end (not shown)and a distal end 104. There is a magnet body 106 inside the distal endportion of the magnetic medical device 100. The magnet body 106 ispreferably made from a strong permanent magnetic material, such asneodymium-iron-boron, or other suitable material. The magnet body 106 istrapped within a cage 108 formed by supports 110 proximal to the magnetbody, and 112 distal to the magnet body. The cage 108 allows the magnetbody 106 to rotate, but substantially restricts axial or radialmovements. The distal face 114 of the support 110 is smoothly, concavelycurved and the proximal face 116 of the support 112 is likewisesmoothly, concavely curved to restrict the axial and radial movement ofthe magnet body 106, while otherwise permitting the magnet body to turn.The magnet body 106 preferably has a smoothly, convexly curved surfaceto facilitate the movement of the magnet body on the faces 114 and 116.As shown in the figures the magnet body 106 is a sphere, but it could besome other shape, such as an elipsoid.

Two pairs of opposing actuator wires 118, 120 and 122, 124 are attachedto the magnet body 106, and extend to the proximal end of the magneticmedical device 100, where they can be operated by pushing and/orpulling. Pulling one actuator wire and/or pushing the other actuatorwire in the pair causes the magnet body 106 to turn. The pairs ofopposing actuator wires 118, 120 and 122, 124 are preferably located inperpendicular planes, and thus by operating the opposing actuator wires,the direction of the magnetic moment of the can sweep a fairly largerange of orientations, as indicated by the 126 cone of the projectedmagnetic moment shown in FIG. 9. Ideally the magnet will be capable ofpointing to all directions in space. Thus, as shown in FIGS. 11A and11B, the magnetic moment of the magnetic body 106, indicated by arrow m,can be moved by operating the actuator wires 118, 120.

Of course, instead of actuator wires 118, 120 and 122, 124, some othermechanism could be used to selectively reorient the magnet body 106. Themechanism can be any other mechanism that can reorient the magnet bodycan be used, and this mechanism preferably allows the magnet body 106 tobe oriented so that the magnet moment can be moved to any selectedorientation with respect to the magnetic medical device 100.

The external magnetic field required to manipulate the catheter iscomparable to that used in “conventional” magnetic guidance, since inboth cases, the catheter magnetic moment is comprised of a strongpermanent magnet.

An alternate construction of the medical device 100 is indicatedgenerally as 100′ in FIGS. 12, 13, and 14. Like medical device 100, themedical device 100′ has a magnet body 106 in its distal end portion.This magnet body is trapped in a cage 108′ formed by supports 110′proximal to the magnet body, and 112′ distal to the magnet body. Thecage 108′ allows the magnet body to rotate, but substantially restrictsaxial or radial movements. The distal face 114′ of the support 110′ issmoothly, concavely curved and the proximal face 116′ of the support112′ is likewise smoothly concavely, curved to restrict the axial andradial movement of the magnet body, while otherwise permitting it toturn. The magnet body 106′ preferably has a smooth curved surface tofacilitate its movement on the faces 114′ and 116′. As shown in thefigures the magnet body 106 is a sphere, but it could be some othershape, such as an elipsoid.

Magnetic medical device 100′, unlike magnetic medical device 100, doesnot have the two pairs of opposing acutator wires 118, 120 and 122, 124for controlling the orientation of the magnet body 106. Instead, medicaldevice 100′ has coils for generating a local magnetic field for changingthe orientation of the magnet body 106. In this alternative constructionof the second preferred embodiment there are preferably three coils 130,132, and 134 which are preferably arranged in three mutuallyperpendicular planes. The coil 130 is preferably embedded in the wall ofthe magnetic medical device 100′ adjacent the distal end 104 and extendscircumferentially around the distal end portion of the magnetic medicaldevice. The coil 130 is generally oriented in a plane 136 transverse tothe axis of the magnetic medical device. The coil 132 is also preferablyembedded in the wall of the magnetic medical device 100′ near the distalend. The coil 132 is generally in a plane 138 parallel to thelongitudinal axis of the magnetic medical device 100′. The coil 134 isgenerally in a plane 140 parallel to the longitudinal axis of the deviceand perpendicular to the plane 136 in which coil 130 lies.

By selectively applying currents to the coils 130, 132, and 134,magnetic fields of virtually any direction can be applied to the magnetbody 106, which tends to align with the local field direction created bythe coils. A locking device can be provided to lock the magnet body 106in its selected orientation, so that the coils 130, 132, and 134 do nothave to remain energized to maintain the selected orientation of themagnetic body, only to change the orientation of the magnetic body tothe selected orientation.

The coils 130, 132, and 134 can have the same construction and number ofturns as discussed above, for coils 26, 28, and 30. With a current of0.1 amps applied to the coils, each can generate a local magnetic fieldof about 0.1 T in an orthogonal direction to orient the permanentmagnet. If this local field exceeds the strength of the externallyapplied navigating magnetic field, the magnet will preferably align withthe local field, and a torque will be applied to the tip of the magneticmedical device 100′ to bring the magnetic moment of the magnet body 106into alignment with the external magnetic field. The magnetic moment ofa permanent magnet, such as magnet body 106, is about ten times largerthan the moment of the local coils 130, 132, and 134, so the orientationof the magnet moment of the magnet body 106 will determine catheteralignment in the externally applied navigating magnetic field. If thelocal field is much less than the externally applied navigating magneticfield, then the magnetic moment of the magnet body 106 will align withthe externally applied navigating magnetic field, independent of thecoil currents, and navigation using the coils will not be possible. Inthis case, the external field can be reduced to a value smaller than thelocal fields to allow the magnetic moment of the magnet body 106 toalign with the local field. The magnet body 106 can then be locked inplace while the external field is ramped up to its desired value. Oncethe magnet body 106 is locked in place, the currents in the local coils130, 132, and 134 can be reduced to zero.

A third embodiment of a magnetic medical device constructed according tothe principles of this invention is indicated generally as 200 in FIGS.15A, 15B, 15C, and 15D. As indicated above, the magnetic medical devicemay be any device that a physician might want to navigate through thebody, such as a catheter, an electrode, a biopsy tool or an endoscope.The device 200 typically has a proximal end (not shown) and a distal end204. There is a magnet body 206 inside the distal end portion of themagnetic medical device 200. The magnet body 206 is preferably made froma strong permanent magnetic material, such as neodymium-iron-boron, orother suitable material. The magnet body 206 is trapped within a age 208formed by a movable support 210 proximal to the magnet body, and a fixedsupport 12 distal to the magnet body. The cage 208 allows the magnetbody to rotate, but substantially limits axial or radial movements. Thedistal face 214 of the support 210 is smoothly, concavely curved and theproximal face 216 of the support 212 is likewise smoothly concavely,curved to restrict the axial and radial movement of the magnet body,while otherwise permitting it to turn. The magnet body 206 preferablyhas a smooth curved surface to facilitate its movement on the faces 214and 216. As shown in the figures the magnet body 206 is a sphere, but itcould be some other shape, such as an elipsoid.

The moveable support 210 can be moved axially proximally away from themagnet body 206 to an unlocked position and distally toward the magnetbody 206 to a locked position in which it pins the magnet body 206against the fixed support 212 to lock the magnet body against movementrelative to the device 200. When the moveable support 210 is moved toits unlocked position proximally away from the magnet body 206 themagnet body can freely move into alignment with an externally anpliedmagnetic field, and when the moveable support 210 is moved to its lockedposition, pinning the magnet body 206 against the support 212, theorientation of the magnet body 206 is locked relative to the device 200,and will not change even if the externally applied magnetic field ischanged.

Alternate locking mechanisms are possible, such as a microballoon, whichis inflated against magnetic 206 to prevent movement

Operation

In operation, the magnetic medical device 20 of the first embodiment isintroduced into the operating region of the patient's body. A relativelystrong magnetic field (between about 0.5 T and about 5 T), ofsubstantially uniform direction (at least within the operating region)is applied to the operating region, preferably with an external sourcemagnet. The external source magnet can be one or more permanent magnets,electromagnets, or superconducting electromagnets. The coils 26, 28, and30 can be selectively energized to create a selected local magneticmoment in the distal end portion of the device 20, which responds to theexternally applied magnetic field, causing the distal end portion of thedevice 20 to move relative to the applied magnetic field. Once in itsdesired orientation, the distal end 24 of the magnetic medical device 20can be advanced. When a further change of direction is desired, thecurrents to the coils 26, 28, and 30 are changed to appropriate valuesto change the direction of the magnetic moment of the magnetic medicaldevice to cause the distal end portion of the magnetic medical device tomove to the desired orientation in the externally applied magneticfield. Through this method of successive orientation of the distal end24 of the magnetic medical device 20, and advancement of the magneticmedical device in the selected direction, the distal end of the magneticmedical device can be navigated anywhere in the body, and particularlythrough body lumens and cavities.

To avoid excessive heating of the coils, the coils are preferably onlyenergized when actively redirecting the magnetic medical device.Alternatively, or in addition, the coils can be energized with a pulsedcurrent. The medical device will have a characteristic recovery time, inwhich the distal end portion of the device “recovers” from being bent.By pulsing the currents in the coils at time intervals shorter than thisrecovery time, the magnetic medical device can be maintained in anorientation without the constant application of current to the coils.For example, in catheters under 3 mm in diameter made of polymericmaterials, typical recovery times for the catheter to straighten from abend can be measured in seconds. By pulsing the current more frequently,the orientation of the catheter can generally be maintained.

In operation, the magnetic medical device 100 of the first constructionof the second embodiment is introduced into the operating region of thepatient's body. A magnetic field (between about 0.05 and about 0.5 T),of substantially uniform direction (at least within the operatingregion) is applied to the operating region, preferably with an externalsource magnet. The external source magnet can be one or more permanentmagnets, electromagnets, or superconducting electromagnets. The magnetbody 106 can be selectively oriented to change the local magnetic momentin the distal end portion of the device 100 by pulling or pushing on theactuator wire pairs 118, 120 and 122, 124, to move the magnet body 106within the cage 108. An optional locking device can be used to lock themagnet body 106 in its selected orientation. The magnet moment of themagnetic medical device 100 responds to the externally applied magneticfield, causing the distal end portion of the device 100 to move relativeto the field. Once in its desired orientation, the distal end 102 of themagnetic medical device 100 can be advanced. When a further change ofdirection is desired, the actuator wire pairs 118, 120 and 122, 124 areagain used to changed the orientation of the magnet body 106 to changethe direction of the magnetic moment of the magnetic medical device 100to cause the distal end portion of the magnetic medical device to moveto the desired orientation in the externally applied magnetic field.Through this method of successive orientation of the distal end of themagnetic medical device 100, and advancement of the magnetic medicaldevice in the selected direction, the distal end of the magnetic medicaldevice can be navigated anywhere in the body, and particularly throughbody lumens and cavities.

While the actuator wires 118, 120 and 122, 124 will usually be able toprovide sufficient force to reorient the magnet body 106 within themagnetic field applied by the external source magnet, in some instancesit may be desirable to remove the external source field while theactuator wires 118, 120 and 122, 124 are being used to reorient themagnetic body 106, and to reapply the external source field after themagnet body has been moved to its selected orientation.

In operation, the magnetic medical device 100′ of the secondconstruction of the second embodiment is introduced into the operatingregion of the patient's body. A relatively strong magnetic field(between about 0.05 T and about 0.5 T), of substantially uniformdirection (at least within the operating region) is applied to theoperating region, preferably with an external source magnet. Theexternal source magnet can be one or more permanent magnets,electromagnets, or superconducting electromagnets. The coils 126, 128,and 130 can be selectively energized to create a selected local magneticfield in the distal end portion of the device 20, to orient the magnetbody 106 in the direction of the field. Once the magnet body 106 is inits desired orientation with respect to the magnetic medical device100′, it can optionally be locked in that position, for example bymoving the proximal support 110 distally to pin the magnet body againstthe distal support 112, or by pulling the distal support proximally, topin the magnet body against the proximal support. Once the magnet body106 is locked in its desired orientation, then the coils 126, 128, and130 can be deenergized, preventing excessive heating of the coils. Themagnetic moment in the distal end of the magnetic medical device 100′responds to the externally applied magnetic field, causing the distalend portion of the device 100′ to move relative to the field. Once inits desired orientation the distal end of the magnetic medical device100′ can be advanced. When a further change of direction is desired, thecurrents to the coils 126, 128, and 130 are changed to appropriatevalues to change the orientation of the magnet body 106 to change thedirection of the magnetic moment of the magnetic medical device 100′ tocause the distal end portion of the magnetic medical device to move tothe desired orientation in the externally applied magnetic field. Themagnet body 106 is then unlocked so that it moves to its desiredorientation relative to the magnetic medical device 100′, therebycausing the magnetic medical device to move to its desired orientationrelative to the applied magnetic field. Through this method ofsuccessive orientation of the distal end of the magnetic medical device100′, and advancement of the magnetic medical device in the selecteddirection, the distal end of the magnetic medical device can benavigated anywhere in the body, and particularly through body lumens andcavities.

By locking the magnet body 106, the coils 126, 128, and 130 only have toremain on while the magnet body is being repositioned, and this reducesthe risk of overheating. While the coils 126, 128, and 130 will usuallybe able to generate a local field sufficient to reorient the magnet body106 within the magnetic field applied by the external source magnet, insome instances it may be desirable to remove the external source fieldwhile the coils 126, 128, and 130 are reorienting the magnetic body, andto reapply the external source field after the magnet body 106 has beenmoved to its selected orientation.

In operation, the magnetic medical device 200 of the third embodiment isintroduced into the operating region of the patient's body. The lockingmechanism is unlocked by moving the support 210 from its locked position(FIG. 15A) to its unlocked position (FIG. 15B) to allow the magnet body206 to move freely in the distal end. The support can be operated with amechanical device such as a push wire (not shown), by fluid pressure, orany other suitable means. A configuring magnetic field F_(c) (betweenabout 0.0005 and about 0.005 T), of substantially uniform direction (atleast within the operating region) is applied to the operating region,preferably with external source magnets. See FIG. 15C. The externalsource magnet can be one or more permanent magnets, electromagnets, orsuperconducting electromagnets. This field F_(c) causes the magnetmoment m of the magnet body 206 to align with it, thereby moving themagnet body to the desired orientation relative to the distal end of thedevice 200 for the planned subsequent navigation. The magnet body 206 isthen locked in its orientation by advancing the support 210. See FIG.15D. A relatively strong navigation magnetic field (between about 0.05 Tand about 0.5 T), of substantially uniform direction (at within theoperating region) is then applied to the operating region, preferablywith the same external source magnet used to apply the configuringmagnetic field. The external source magnet can be one or more permanentmagnets, electromagnets, or superconducting electromagnets. The magneticmoment in the distal end of the magnetic medical device 200 generated bythe magnet body 206 responds to the externally applied magnetic field,causing the distal end portion of the device 200 to move relative to thefield. Once in its desired orientation the distal end 204 of themagnetic medical device 200 can be advanced. When a further change ofdirection is desired, the applied navigating field can be removed, andthe magnet body 206 unlocked. A configuring field can then be applied inappropriate direction to achieve the desired new orientation, and themagnet body 206 again locked. The configuring field is removed, and thenavigating field reestablished to cause the distal end 204 of themagnetic medical device 200 to move to the desired orientation in theexternally applied magnetic field. Through this method of successiveorientation of the distal end of the magnetic medical device 200, andadvancement of the magnetic medical device in the selected direction,the distal end of the magnetic medical device can be navigated anywherein the body, and particularly through body lumens and cavities.

This magnetic medical device can also be used with a variable externallyapplied navigating magnetic field. However, the ability to reorient themagnetic moment of the magnetic medical device, allows greater freedomof navigation, for example where further changes to the navigatingmagnetic field are difficult or precluded, as might happen where themagnet were close to the patient and could not be moved further, themagnetic moment in the medical device can be changed so that a differentnavigating magnetic field, that the external source magnet can generate,can be used.

What is claimed is:
 1. A method of navigating an elongate medical devicewithin an operating region in the body of a patient, the medical devicehaving a proximal end, a distal end, and at least one coil adjacent thedistal end for creating a magnetic moment of variable direction relativeto the device, the method comprising: introducing the distal end of themedical device into the operating region in the patient's body, themedical device having at least two coils adjacent the distal end of themagnetic medical device; establishing a navigating magnetic field in theoperating region; circulating a cooling fluid through the medical deviceto cool the at least one coil therein; selectively energizing the atleast one coil adjacent the distal end of the elongate medical device tocreate a magnetic moment at the distal end of the elongate medicaldevice to turn the distal end of the elongate medical device in thedesired direction.
 2. The method according to claim 1 wherein there arethree coils adjacent the distal end of the magnetic medical device. 3.The method according to claim 2 wherein there are three coils spacedaround the circumference of the magnetic medical device.
 4. The methodaccording to claim 1 wherein at least one coil extends around thecircumference of the magnetic medical device and at least one coilextends longitudinally.
 5. The method of claim 1 in which the coolingfluid is circulated through a fluid reservoir.
 6. The method of claim 5further comprising cooling the cooling fluid in the reservoir.
 7. Amethod of navigating an elongate medical device within an operatingregion in the body of a patient, the medical device having a proximalend, a distal end, and at least one coil adjacent the distal end, themethod comprising: introducing the distal end of the medical device intothe operating region in the patient's body; establishing a navigatingmagnetic field in the operating region; circulating a cooling fluidthrough the medical device to cool the at least one coil therein;selectively energizing the at least one coil adjacent the distal end ofthe elongate medical device to create a magnetic moment at the distalend of the elongate medical device to turn the distal end of theelongate medical device in the desired direction; and circulatingcooling fluid [is circulated] to maintain the surface of the medicaldevice below about 50° C.
 8. The method according to claim 7 whereincooling fluid is circulated to maintain the surface off the medicaldevice below about 45° C.